1. Field of the Invention
The present invention relates to an electrophotographic image forming method. Specifically, the present invention relates to an image forming method comprising electrostatically charging the surface of an image bearing member in association with discharging in a charging step, forming an electrostatic latent image on the surface of the image bearing member in an exposing step, and developing the electrostatic latent image by a developer.
2. Description of the Related Art
In the image forming method used for electrophotographic apparatuses and electrostatic recording apparatuses are known a variety of methods for forming a latent image on an image bearing member such as an electrophotographic photosensitive member and an electrostatic recording dielectric medium.
For example, usually, the electrophotography uniformly charges a photosensitive member as a latent image bearing member using a photoconductive substance to a desired polarity and potential, and performs image pattern exposure to form an electric latent image. Then, the electric latent image is developed with a toner to form a visualized image, which is then transferred onto a transfer medium such as paper and fixed.
Recently, network-capable multifunction machines including all the output terminals such as a copier, a printer and a fax machine have been widely accepted in the market.
While the electrophotographic system is widely accepted as such a network-capable output terminal, examples of significant problems include a duty cycle of the main body. The duty cycle refers to the limit number of sheets by which the main body normally continues operating without maintenance by a worker.
Factors determining the duty cycle can include the life span of the image bearing member (photosensitive member). A longer life span of the photosensitive member can increase the duty cycle to improve reliability. Additionally, wastes can be reduced. From the viewpoint of environmental protection, development of such a technique is demanded.
In such a situation, highly durable photosensitive members such as amorphous silicon (a-Si) photosensitive members and organic photosensitive members having a protective layer made of a curable resin on the surface thereof have been increasingly used as the photosensitive member.
Unfortunately, because the highly durable photosensitive member is used for a long time for its high durability, the surface of the photosensitive member may be deteriorated, affecting the quality of the image.
The surface of the photosensitive member is deteriorated by fine paper powder produced from pieces of paper often used as a transfer material, an organic component originating from the paper powder, and a discharge product caused by a high-voltage member present in the apparatus using the photosensitive member. The fine paper powder, organic component or discharge product attached to the surface of the photosensitive member may make the electric resistance of the photosensitive member lowered particularly under a highly humid environment to interfere with formation of a sharp electrostatic latent image, leading to deterioration in the quality of the image.
Moreover, electric discharging by a charging apparatus may change the quality of the surface itself of the photosensitive member, leading to increased hydrophilicity. In this case, moisture is adsorbed to the areas of the photosensitive member with increased hydrophilicity to reduce the electric resistance, thereby interfering with formation of a sharp electrostatic latent image.
Also in the case where the image bearing member is an intermediate transfer member, the surface may be deteriorated by the influence of the paper powder or discharge product to tend to reduce the transfer performance of toner or cause toner fusing and insufficient cleaning of the image bearing member.
There is a method of removing a deteriorated surface portion of an image bearing member (particularly, photosensitive member) with the aid of a scraping member or a polishing agent to suppress the occurrence of problems. In this case, a method of externally adding a material having a high polishing ability to a toner to polish the photosensitive member surface is often used (see Japanese Patent Application Laid-Open No. 2008-304788). In the method by which the photosensitive member is scraped, however, the life span of the surface of the photosensitive member is likely to be reduced.
On the other hand, there is a method of coating a surface of a photosensitive member with a fatty acid metallic salt or the like as a protector, thereby to prevent image deletion (see Japanese Patent Application Laid-Open No. 2008-122593). Unfortunately, in the method using the photosensitive member protector, contamination of other apparatuses such as the charging apparatus and the developing apparatus by the photosensitive member protector may have a large influence to often reduce the life span of the apparatuses other than the photosensitive member. Moreover, if a discharge product is formed, the photosensitive member protector tends to be deteriorated to increase the adhesive force thereof. Accordingly, as the life span of the photosensitive member is prolonged, accumulation of the photosensitive member protector needs to be more cared.